Conventional earth current leakage circuit breakers and over-current fuses are commonly deployed to prevent injuries to people and property from dangerous conditions resulting from, for example, current leakages or fires resulting from electrical faults.
Such devices typically detect the occurrence of certain types of electrical faults to prevent harm to persons and property. However, when such conventional devices are employed, some electrical faults may not be detected and such devices may falsely detect electrical faults where none exist. Such errors may be due to the lack of intelligent ground fault identification systems in conventional devices.
Ground faults may be commonly defined as the existence of a current imbalance between the supply and the return path wherein an undesirable and significant amount of the unreturned current is leaking, or passing through an object—for example a human body, to the ground. Notably, the passage of electrical current through the human body may cause injury or even death.
Underwriters Laboratories (UL), an American Worldwide Safety Consulting and Certification Organization, provides criteria that GFCIs and similar devices must meet in order to qualify as approved ground fault detection devices. Such criteria may further require GFCIs and similar devices to avoid false detection of ground faults when provided with current draws that may resemble ground faults, such as back-EMF noise or certain pulsed current draws.
Because the failure to detect an actual ground fault may result in serious safety hazards, conventional apparatuses typically are typically over-inclusive when determining the presence of a ground fault. Such conventional apparatuses do not provide for analysis or investigation of the nature of the leakage waveform. While erring on the side of determining that electrical faults exist may have beneficial safety effects, this may increase the frequency of both false positives of ground fault detection and unnecessary tripping of GFCIs.
Certain electrical appliances and apparatuses may draw current in a manner that may resemble ground fault phenomena, at least when observed by conventional GFCIs and similar devices. For example, certain electrical appliances may generate back-EMF noise or exhibit other irregular current drawing behavior during normal operation. Thus, a conventional electrical protection circuit that determines the presence of a ground fault merely based on the existence of an unbalanced current condition may falsely detect ground faults. Accordingly, conventional electronic fault detection systems that do not perform a more detailed analysis of a leakage waveform may disturb the normal operation of electrical appliances by the false detection of electrical faults and by inappropriately tripping electrical safety circuits. Such conventional electronic fault detection systems may also be out of compliance with UL or other regulatory requirements.
While it may be desirable to have GFCIs and other electronic fault detection systems engage in a more detailed analysis of a fault detection waveform in order to reduce occurrences of false fault detection and inappropriate tripping, it may also be important that any such analytic processing algorithm accurately identify a leakage waveform so that it will not fail to detect a true ground fault or other qualifying current leakage condition. Thus, an in-depth analysis of a leakage signal waveform and its analytic signature may provide useful information and parameters to make an accurate and safe determination as to whether a ground fault truly exists.
Therefore, there is a need to be able to identify and detect true ground faults, while also accommodating the operation of certain electrical appliances that may be characterized by unusual current draws. More specifically, it may be desirable to distinguish actual ground faults from other unusual current draws by evaluating and characterizing a current leakage waveform.
Additionally, there remains a need for a tripping mechanism to ensure a proper, flexible trip operation at the time desired. There further remains a need for such a tripping mechanism to provide automatic and/or manual testing functionality to ensure that the GFCI and/or other electrical protection devices work properly.